Antimicrobial agents is just one category of therapeutic agents in which many individual agents are comparable. In fact, antibiotics are not so comparable; each agent has different potentials, especially in terms of clinical indications defined by the causal microorganisms and ecological impact. Thus, proper identification of the cause of infection is essential to learn along with the differences between the various categories of antimicrobial agents; classes, and sometimes between subclasses or individual agents, to optimize their usage.
Categories of Antimicrobial Agents
A variety of antimicrobial agents have been developed to protect humans from infection or disease. Some of these are derived from other microbes (fungi or bacteria), some are plant derivatives, and the others have been synthesized in the laboratory (Saleem et al., 2010, p.238). Most of the antimicrobial agents attempt to target differences between the microbe and humans in order to lessen toxicity to the host. These antimicrobial agents kill the microbes or inhibit their growth. The major families of antibiotics discovered include penicillins, cephems, aminoglycosides, tetracyclines, macrolides, peptide antibiotics, chloramphenicol, ansamycins, and lincosamides, as well as synthetic antibacterial agents, such as the benzylpyrimidines (trimethoprim), fluoroquinolones, fosfomycin, penems (ritipenem and fropenem [faropenem]), and 5-nitroimidazoles (metronidazole and derivatives). The classifications within each family are complex.
Viral and Bacterial Infections
The major differences between viral and bacterial infections are, of course, the infectious agents. If the infectious agent is a virus, then it is viral infection, and if the agent is a bacteria, then it is a bacterial infection. Similarly, these infections are caused by microbes or living organisms that are too small to be viewed individually without magnification.
Bacteria are typically small, unicellular prokaryotes surrounded by cell walls containing peptidoglycan. They take a variety of shapes, including spheroid or ovoid (cocci, such as Streptococcus), rod-like (bacilli such as E. coli), and corkscrewlike (spirochetes, such as Borellia burgdorferi, the causative agent of Lyme disease). Bacteria have differential reactions to various staining procedures. A commonly used stain is the gram stain, which divides bacteria into gram-positive (organisms appear purple) and gram-negative (organisms appear pink) (Thomson & Miller, 2011).
Viruses, like bacteria, may act as infectious agents of human disease. On the other hand, viruses (virus is Latin for “poison”) are the tiny agents that pass through most filters. They do not consist of cells but rather are collections of nucleic acid (DNA or RNA) in a core surrounded by a protein coat and sometimes an envelope. Viruses carry out some, but not all, of the normal processes of life. Viral diseases include AIDS, yellow fever, hepatitis, hemorrhagic fevers, influenza, polio, and the common cold. Important distinctions exist in the manner, in which viruses and bacteria are killed (Krummenacher, et al., 2011).
Viruses, unlike bacteria, are not killed by antibiotics but may be killed by interferons (chemical agents produced by the host immune cells). A number of antiviral agents have been developed recently, including ribaviran and zidovudine (AZT, used to treat HIV infection) (Scourfield et al., 2011). In addition to causing infectious diseases, viruses may initiate cancer. About 10% of human cancers are of viral origin. Some cancer-causing viruses are HTLV-1 (acute T cell leukemia), papillomaviruses (cervical cancer), Epstein-Barr virus (Burkitt’s lymphoma), hepatitis B and C (liver carcinoma), and human herpesvirus-8 (Kaposi’s sarcoma) (Ji et al., 2011, pp. 2773-2778).
Proper Identification and Selection
Awareness of new infections is achieved due to the improved detection and proper identification of the underlying causes of illness in order to select the proper antimicrobial agent. Engelkirk and Duben-Engelkirk (2010) state “the diseases are divided by type of causative agent: bacteria, viruses, protozoa, or infectious protein” (p.125). Proper identification of the infection includes the history and the causative agents and is the key to selecting the proper antimicrobial agent.
Many of the emerging diseases, however, appear to be entirely new to humans, while many re-emerging diseases represent increasing threats to humankind. Several of the factors believed to contribute to the emergence or re-emergence of infectious diseases include microbial evolution, the trend toward increasing urbanization, population migrations between regions or into formerly uninhabited areas, the ease and speed of long-distance movement of persons and materials, natural disasters, climatic and ecological changes, and decreased vaccination rates in many regions of the world. One of the important factors contributing to the rapid emergence of new infections is the increasingly large numbers of immunocompromised individuals who are vulnerable to the development of severe or life-threatening diseases as a result of infection by organisms formerly viewed as nonpathogenic (Saleem, et al., 2010, pp. 236-245).
In the case of HIV, Krummenacher et al. (2011) cited several types of antiretroviral agents, in the form of 26 drugs licensed for the treatment of HIV infection. The earliest drugs acted as reverse transcriptase inhibitors and included AZT and stavudine, which are nucleoside analogues. In addition to killing HIV, these drugs are also toxic to the mitochondria in human cells and may cause muscle pain, weakness, fatigue, loss of body fat, and lactic acidosis. Non-nucleoside reverse transcriptase inhibitors, such as etravirine and efavirenz, are also available (pp.550-555).
Antimicrobial agents have had a great impact on human history, as well as the vast numbers of emerging and reemerging infectious diseases that have either been discovered during the past four to five decades or have greatly increased in incidence or virulence regionally or worldwide during that time. Hence, it is important to identify correctly the cause of infection in order to select properly the right antimicrobial agent.
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Ji, X, Wang, Z, Geamanu, A, Sarkar, F H, Gupta, S V. (2011). Inhibition of cell growth and induction of apoptosis in non-small cell lung cancer cells by delta-tocotrienol is associated with notch-1 down-regulation. Journal of Cellular Biochemistry, 112(10), 2773-2783.
Krummenacher, I., Cavassini, M., Bugnon, O., & Schneider, M. (2011). An interdisciplinary HIV-adherence program combining motivational interviewing and electronic antiretroviral drug monitoring. AIDS Care, 23(5), 550-561.
Saleem, M., Nazir, M., Ali, M. S., Hussain, H., Lee, Y. S. (2010). Antimicrobial natural products: an update on future antibiotic drug candidates. Natural Product Reports, 27(2), 238-254.
Scourfield, A., Waters, L., & Nelson, M. (2011). Drug combinations for HIV: Whats new? Expert Review of Anti-Infective Therapy, 9(11), 1001-1011.
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